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The tattooed neo-Nazi musician and Army veteran suspected of killing six people in the Sikh temple rampage died after shooting himself in the head, the FBI said on Wednesday.

Although detectives have combed through Wade Michael Page’s email, interviewed more than 100 people and recovered hundreds of pieces of evidence at Page's home and the site of the mass killing at the temple outside Milwaukee, feds said they have not yet “clearly defined a motive.”

Scenes from the Sikh Temple Shooting

"We may never know exactly why he chose that facility, that entity, at that time," said Steven Conley, assistant agent in charge of national security for the FBI in Milwaukee. "We're trying to piece together, and eventually we will piece together as much as we can."

"We will have a good idea of the motive by the time this investigation is done," he added. "But again, why that building, that temple, at that time, that may have died with Page."

At the moment, detectives are sifting through the gunman's life, assembling the biography of a man who apparently had few relatives, a spotty work history and a thin criminal record. The FBI's agent in charge in Milwaukee, Teresa Carlson, said investigators have not linked anyone else to the attack or found any kind of note left by Page.

The Sikh community holds out hope.

"We just want to get to the bottom of what motivated him to do it," said Amardeep Singh, an executive with the New York-based Sikh Coalition. "It's important to acknowledge why they lost their lives."

Page, a 40-year-old Army veteran, opened fire with a 9 mm pistol at the Sikh Temple of Wisconsin shortly before Sunday services. The dead included temple President Satwant Singh Kaleka, who was shot as he tried to fend off the shooter with a butter knife.

Page shot a responding police officer at least eight times in the parking lot before another officer wounded Page in a shootout. Police had earlier said Page was killed by the officer, but Carlson said Wednesday that Page shot himself after being hit and died of the self-inflicted wound.

At a new conference on Wednesday, Oak Creek's police chief said the officer who was shot eight to nine times while attending to a temple shooting victim is improving at a Milwaukee area hospital. Lt. Brian Murphy was sitting up and walking, Police Chief John Edwards said.

Two others injured in the temple shooting rampage are still in critical condition and in the intensive care unit at Frodtert Hospital, spokeswoman Kathy Sieja said.

President Barck Obama called Indian Prime Minister Manmohan Singh Wednesday to express condolences for the deaths; some of the Sikh worshippers were from India.

White House press secretary Jay Carney said the two leaders discussed their "shared commitment to tolerance and religious freedom" and the president reiterated his appreciation of the contributions that Sikhs make in the U.S.

Singh is India's first prime minister from the Sikh faith.

Meanwhile, the fragments of Page's past that have emerged suggest he lived a somewhat troubled life.

A native of Littleton, Colo., he had a record of minor alcohol-related crimes in Texas, Colorado and North Carolina. He was demoted during a stint in the Army for getting drunk on duty and going AWOL before he was discharged in 1998. Page eventually moved to Wisconsin, living in South Milwaukee with a girlfriend and working third-shift at a brazing factory in Cudahy, another Milwaukee suburb.

Neighbors said the couple broke up this past spring. Page moved into a Cudahy duplex in mid-July and quit showing up for work around the same time. A few days after he moved into the duplex, he visited a West Allis gun shop and, after clearing background checks, bought the gun he used in the shooting.

The Southern Poverty Law Center has described Page as a "frustrated neo-Nazi" who participated in the white-power music scene, playing in bands called Definite Hate and End Apathy.

Rajwant Singh, chairman of the Sikh Council on Religion and Education, said even though Page is dead, other white-supremacy and neo-Nazi groups could harbor similar intentions.

"Our concern is, how do we tackle these hate groups operating underground or in darkness?" he said.

The FBI has classified the incident as domestic terrorism, a violent act for social or political gain. The FBI's Carlson said though investigators have not yet determined what drove Page over the edge or that anyone nudged him along the way, they continue to search to make sure.

Investigators probably will collect all bullets and fragments from the temple and the victims' bodies to confirm they came from Page's gun. Detectives also will pore over witness statements to make absolutely certain he was the only shooter, said Joe LeFevre, chairman of the forensic science department at Fox Valley Technical College in Appleton.

Authorities are interviewing Page's family, friends and associates. Agents spent Monday morning doing a door-to-door sweep on his street, chatting with neighbors on their front porches and in their backyards.

"It's like any crime," said Jack Ryan, a Rhode Island attorney who trains police around the country. "You focus on their recent tracks. You focus on friends, acquaintances. He had to get ready for this plot somewhere."

The investigation could take weeks or longer. But Page's motive is the key.

If detectives determine Page simply held a personal grudge, the Sikhs and the rest of the public will have an answer. If investigators conclude he was motivated by racist ideology, that might lead police to accomplices, help collect intelligence on white supremacist groups and prevent future attacks.

Page's girlfriend, 31-year-old nursing student Misty Cook, faced some legal trouble herself, though Carlson said Wednesday that her arrest over the weekend was not connected to the shootings. Cook was arrested on a weapons violation Sunday after investigators interviewed her about Page, but Carlson said she was cooperative and was quickly released.

South Milwaukee police had said Cook was taken into custody on a tentative charge of being a felon in possession of a firearm. Milwaukee County sheriff's spokeswoman Fran McLaughlin says the 31-year-old Cook also went by Brenda Cook. Online court records show that Brenda Cook pleaded no contest in 2005 to a felony charge of fleeing an officer.

The voicemail on Cook's cellphone was full and wouldn't accept a message. However, in regard to the shooting, she told the Milwaukee Journal Sentinel in an email: "If I could say something to ease the pain of the victims and their families, I would gladly do so. Unfortunately, words do not begin to heal the pain they are going through."

No matter how thorough the investigation, the final conclusions are bound to leave victims with many of the same anguish-filled questions.

"Whatever the answer is, we can be reasonably sure it won't be an answer many people would say makes sense to them," said University of Wisconsin-Madison law professor Michael Scott, who is writing a guidebook for police on hate crimes.

"We'd like to have some peek into that twisted mind. But in the end, it's still a peek into a twisted mind that doesn't tell us anything we didn't already know about human nature."